U.S. patent application number 13/389333 was filed with the patent office on 2012-05-31 for bioreactor comprising a silicone coating.
This patent application is currently assigned to Wacker Chemie AG. Invention is credited to Christoph Muller-Rees, Rupert Pfaller.
Application Number | 20120135514 13/389333 |
Document ID | / |
Family ID | 43429981 |
Filed Date | 2012-05-31 |
United States Patent
Application |
20120135514 |
Kind Code |
A1 |
Muller-Rees; Christoph ; et
al. |
May 31, 2012 |
Bioreactor Comprising A Silicone Coating
Abstract
The invention relates to a bioreactor for cultivating
phototrophic organisms in an aqueous culture medium. The reactor
parts and/or fittings that come into contact with the culture
medium are entirely or partially coated with a silicone layer, and
the surface of the silicone layer has a contact angle to the water
of at least 100.degree..
Inventors: |
Muller-Rees; Christoph;
(Pullach, DE) ; Pfaller; Rupert; (Muenchen,
DE) |
Assignee: |
Wacker Chemie AG
Munich
DE
|
Family ID: |
43429981 |
Appl. No.: |
13/389333 |
Filed: |
August 6, 2010 |
PCT Filed: |
August 6, 2010 |
PCT NO: |
PCT/EP10/61491 |
371 Date: |
February 7, 2012 |
Current U.S.
Class: |
435/304.1 ;
435/289.1; 435/305.1; 524/588 |
Current CPC
Class: |
C12M 21/02 20130101;
C12M 39/00 20130101 |
Class at
Publication: |
435/304.1 ;
435/289.1; 435/305.1; 524/588 |
International
Class: |
C12M 1/00 20060101
C12M001/00; C09D 183/04 20060101 C09D183/04; C09D 183/07 20060101
C09D183/07; C12M 1/24 20060101 C12M001/24 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 7, 2009 |
DE |
10 2009 028 338.2 |
Claims
1. A bioreactor for cultivating phototrophic organisms in an
aqueous culture medium, in which the reactor parts that come into
contact with the culture medium are coated completely or partially
with a silicone layer, wherein the surface of the silicone layer
has a contact angle with water of at least 100.degree..
2. The bioreactor as claimed in claim 1, wherein the bioreactor is
a closed reactor.
3. The bioreactor as claimed in claim 1, wherein the bioreactor is
a plate-type bioreactor, tubular bioreactor, (bubble) column
bioreactor or hose-type bioreactor.
4. The bioreactor as claimed in claim 1, wherein the bioreactor is
made of transparent or translucent materials.
5. The bioreactor as claimed in claim 1, wherein the reactor parts
are coated with a transparent or translucent silicone layer.
6. The bioreactor as claimed in claim 1, wherein the silicone layer
contains one or more silicones selected from the group consisting
of condensation-crosslinking silicone elastomers,
addition-crosslinking silicone elastomers, silicone hybrid
polymers, silicone resins and silicone gels.
7. A method for providing bioreactor with an antifouling coating,
wherein the bioreactor is coated, on the reactor parts coming into
contact with a culture medium, completely or partially with a
silicone layer, and the surface of the silicone layer has a contact
angle with water of at least 100.degree..
8. A method of providing a bioreactor with an antifouling coating,
comprising applying to the bioreactor a film of silicone whose
surface has a contact angle with water of at least 100.degree..
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the national phase filing of
international patent application No. PCT/EP2010/061491, filed 6
Aug. 2010, and claims priority of German patent application number
10 2009 028 338.2, filed 7 Aug. 2009, the entireties of which
applications are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to a bioreactor that is provided with
an antifouling coating, method of providing bioreactors with an
antifouling coating, and the use of silicones for providing
bioreactors with an antifouling coating.
BACKGROUND OF THE INVENTION
[0003] The economic cultivation of phototrophic microorganisms
(microalgae, cyanobacteria, purple bacteria) on an industrial scale
has not yet been solved, owing to the problems of light supply,
monoseptic culture conditions and scaling-up. To date, no universal
standard system is available for the large-scale cultivation of
phototrophic microorganisms. Of the many tens of thousands of
representatives of phototrophic microorganisms, at present only a
few dozen are produced in relatively large amounts, and these are
generally produced in open systems, which are not free from
contamination. To date, the culture conditions of phototrophic
microorganisms, in pilot-scale production in closed reactors,
cannot be kept constant for an extended period, as the phototrophic
microorganisms that form in a culture phase are deposited on the
reactor walls, which leads to fluctuations in the amount of light
supplied to the culture medium and to variable mixing of the
culture medium. Algal deposits are often caused by stress
conditions (e.g. through shearing) during cultivation, the causes
of which can be uncontrolled growth conditions (e.g. light,
temperature in open-pond and closed reactors) of the microorganisms
or induction of the production of valuable substances by the
phototrophic organisms (e.g. astaxanthin, beta-carotene).
[0004] A closed photobioreactor for cultivating algae is known from
WO 2008/055190 A2. The materials used are glass or plastics such as
polyethylene, PET, polycarbonate. Detaching microorganisms from the
surfaces of bioreactors by means of ultrasound is described in DE
10 2005 025 118 A1. In US 2003/0073231 A1 and US 2007/0048848 A1,
deposits are removed by mechanical means, for example brushing.
These are relatively laborious methods, which are not arbitrarily
scalable. In DE 44 16 069 A1 it is recommended to provide
light-conducting fibers used for illuminating bioreactors with a
smooth surface. US 2008/0311649 A1 proposes increasing the flow
rate of the algae-containing medium in tubular bioreactors, to
prevent deposition of the algae. This has the disadvantage that the
culture parameters with respect to flow rate can no longer be set
independently.
[0005] In WO 2008/132196 A1, crosslinkable
polyorganosiloxane-polyoxyalkylene copolymers are recommended as
antifouling coating in the marine area, in particular for coating
metal or concrete, for example ships' hulls, buoys, drilling rigs.
Later in this publication there is discussion of GB 1307001, which
describes the coating of hulls with silicone resins to prevent
fouling, and of U.S. Pat. No. 3,702,778, which describes the
coating of hulls with silicone rubber. It can be seen from WO
2008/132196 A1 that in both cases effective prevention of fouling
is only achieved at relatively high flow rate on the hull. To
prevent fouling of underwater structures, it is recommended in WO
01/94487 A2 to apply glass-like interpenetrating polymer networks
based on silanol-terminated silicones and alkoxy-functionalized
siloxanes, together with two separable agents, at least one of
which grafts onto the glass matrix. Silicone coatings are described
in this document as being unstable in a marine environment, with
the disadvantage that the coating must be renewed frequently. In
Biofouling, 2007, 23(1), 55-62 it is recommended to apply
silicone-based antifouling paint films on hulls in particular
patterns. Paints that only contain silicones are described as not
inherently antifouling. In WO 2008/145719 A1, transparent LED
plastic moldings are used for illuminating photoreactors. For this,
it is preferable to use moldings in which LEDs are embedded in a
silicone molded article.
SUMMARY OF THE INVENTION
[0006] Against this background, the problem to be solved was to
improve bioreactors for cultivation of microorganisms, so that
fouling with microorganisms on the reactor parts coming into
contact with the culture medium is largely prevented, and any
fouling that does occur can be removed inexpensively. The solution
should not have a negative effect on product quality, it should be
up-scalable, and should be capable of universal application,
independently of the process parameters required for
cultivation.
[0007] The invention relates to a bioreactor for cultivating
phototrophic organisms in an aqueous culture medium, in which the
reactor parts and/or reactor fittings that come into contact with
the culture medium are coated completely or partially with a
silicone layer, wherein the surface of the silicone layer has a
contact angle with water of at least 100.degree..
DETAILED DESCRIPTION OF THE INVENTION
[0008] The bioreactor is suitable for the cultivation of
phototrophic macro- or microorganisms. Phototrophic organisms are
designated as those that require light and carbon dioxide, or
optionally another carbon source as well, for growth. Examples of
phototrophic macroorganisms are macroalgae, plants, mosses, plant
cell cultures. Examples of phototrophic microorganisms are
phototrophic bacteria such as purple bacteria and phototrophic
microalgae including cyanobacteria. Preferably the bioreactor is
used for the cultivation of phototrophic microorganisms, especially
preferably the cultivation of phototrophic microalgae.
[0009] The bioreactor can be a closed reactor or an open reactor,
in each case of any desired shape. For example, in the case of open
reactors it is possible to use tanks or so-called "open ponds" or
"raceway ponds". Closed reactors are preferred as bioreactors. The
closed bioreactors can be for example plate-type bioreactors,
tubular bioreactors, (bubble) column bioreactors or hose-type
bioreactors. Plate-type bioreactors consist of perpendicular or
slanting brick-shaped plates, with a large number of plates joined
together to form a relatively large reactor system. Tubular
bioreactors consist of a tube system, which can be arranged
vertically or horizontally or at any angle in between, and the tube
system can be very long, preferably up to several hundred
kilometers. The culture medium is then transported through the tube
system, preferably by means of pumps or by the air-lift principle.
The column bioreactor consists of a closed, cylindrical vessel,
which is filled with the culture medium. In bioreactors of this
type, a mixture of air and carbon dioxide or also carbon dioxide is
introduced, and the ascending bubble column provides mixing of the
culture medium. Hose-type reactors comprise a reactor system that
consists of a single hose of any length or a large number of hoses
of any length.
[0010] The bioreactors are preferably made of transparent or
translucent materials. Transparent materials are those that let
through at least 80% of the light in the spectral range from 400 nm
to 1000 nm. Translucent materials are those that let through at
least 50% of the light in the spectral range from 400 nm to 1000
nm, for example glass or plastics such as polymethylmethacrylate
(Plexiglas), polyesters such as PET, polycarbonate, polyamide,
polystyrene, polyethylene, polypropylene, polyvinyl chloride. For
nontransparent photobioreactors it is possible to use the aforesaid
plastics, but also steel or special steel. Reactor volumes of any
size can be selected.
[0011] Reactor parts mean the reactor walls including reactor
bottom and reactor cover and structure-forming elements in the
culture medium, e.g. baffles. In tubular, plate-type and hose-type
reactors, the tubes, plates and hoses correspond to the reactor
walls.
[0012] The bioreactors are equipped with reactor fittings; for
example, with feed lines for filling and supply of nutrients, and
with discharge lines for product separation and discharge. For
cooling and heating, the bioreactors can optionally be equipped
with heating/cooling devices such as heat exchangers. Moreover, the
bioreactors can also contain stirring devices and pumps for mixing.
Bioreactors are often also equipped with devices for artificial
illumination. Further examples of reactor devices are measuring and
control instruments for monitoring operation.
[0013] Silicones suitable for providing bioreactors with an
antifouling coating are for example condensation-crosslinking
silicones (silicone rubbers), addition-crosslinking silicones
(silicone rubbers), silicone hybrid polymers, silicone resins
and/or silicone gels, provided the surface of the films thereof has
a contact angle of at least 100.degree. with water. Transparent or
translucent silicones are preferred. Transparent silicones are to
be understood as silicones whose films, as a coating with a layer
thickness of 10 .mu.m, let through at least 80% of the light in the
spectral range from 400 nm to 1000 nm. Translucent silicones are to
be understood as those whose films, as a coating with a layer
thickness of 10 .mu.m, let through at least 50% of the light in the
spectral range from 400 nm to 1000 nm.
[0014] Condensation-crosslinking silicone rubber systems
contain
[0015] a) organopolysiloxanes with condensable end groups,
[0016] b) optionally per molecule, at least three organosilicon
compounds having silicon-bonded hydrolyzable groups, and
[0017] c) condensation catalysts.
[0018] Suitable crosslinked silicone rubbers, which crosslink by a
condensation reaction, are room-temperature crosslinking
1-component systems, so-called RTC-1 silicone rubbers. The RTC-1
silicone rubbers are organopolysiloxanes with condensable end
groups, which in the presence of catalysts undergo crosslinking by
condensation at room temperature. The commonest are dialkyl
polysiloxanes of structure
R.sub.3SiO[--SiR.sub.2O].sub.n--SiR.sub.3 with a chain length of
n>2. The alkyl residues R can be identical or different and
generally have 1 to 4 carbon atoms and can optionally be
substituted. The alkyl residues R can also be partially replaced
with other residues, preferably with aryl residues, which
optionally are substituted, and where the alkyl (aryl) groups R are
partially exchanged with groups capable of condensation
crosslinking, for example alcohol (alkoxy system), acetate (acetic
acid system), amine (amine system) or oxime residues (oxime
system). Crosslinking is catalyzed by suitable catalysts, for
example tin or titanium catalysts.
[0019] Suitable crosslinked silicone rubbers, which crosslink by a
condensation reaction, are also room-temperature crosslinking
2-component systems, so-called RTC-2 silicone rubbers. RTC-2
silicone rubbers are obtained by condensation crosslinking of
organopolysiloxanes multiply substituted with hydroxyl groups in
the presence of silicic acid esters. As crosslinking agent, it is
also possible to use alkyl silanes with alkoxy (alkoxy system),
oxime (oxime system), amine (amine system) or acetate groups
(acetic acid system), which crosslink in the presence of suitable
condensation catalysts, for example tin or titanium catalysts, with
the hydroxyl group-terminated polydialkylsiloxanes.
[0020] Examples of the polydialkylsiloxanes contained in RTC-1 and
RTC-2 silicone rubber are those with the formula
(OH)R.sub.2SiO[--SiR.sub.2O].sub.n--SiR.sub.2 (OH) with a chain
length of n>2, wherein the alkyl residues R can be identical or
different, and the R residues have the meaning given above.
Preferably the polydialkylsiloxanes contain terminal OH groups,
which crosslink at room temperature with the silicic acid esters or
the system alkyl silane/tin(titanium) catalyst.
[0021] Examples of the alkyl silanes (with hydrolyzable groups)
contained in RTC-1 and RTC-2 silicone rubbers are those with the
formula R.sub.aSi(OX).sub.4-a, with a=1 to 3 (preferably 1), and X
in the meaning of R' (alkoxy system), C(O)R' (acetic acid system),
N.dbd.CR'.sub.2 (oxime system) or NR'.sub.2 (amine system), where
R' denotes a monovalent hydrocarbon residue with 1 to 6 carbon
atoms.
[0022] Addition-crosslinking silicone rubber systems contain
[0023] a) organosilicon compounds which have residues with
aliphatic carbon-carbon multiple bonds,
[0024] b) optionally organosilicon compounds with Si-bonded
hydrogen atoms or instead of a) and b)
[0025] c) organosilicon compounds which have residues with
aliphatic carbon-carbon multiple bonds and Si-bonded hydrogen
atoms,
[0026] d) the addition of Si-bonded hydrogen to catalysts promoting
aliphatic multiple bond formation and
[0027] e) optionally the addition of Si-bonded hydrogen to agents
delaying aliphatic multiple bond formation at room temperature.
[0028] Suitable addition-crosslinked silicone rubbers are
room-temperature crosslinking 1-component systems, so-called
addition-crosslinking RTC-1 silicone rubbers, room-temperature
crosslinking 2-component systems, so-called addition-crosslinking
RTC-2 silicone rubbers or also room-temperature crosslinking
multicomponent systems. The crosslinking reaction can be initiated
cationically, by means of corresponding catalysts, or radically, by
means of peroxides, or by radiation, in particular UV radiation, or
thermally.
[0029] Addition-crosslinking RTC-2 silicone rubbers are obtained by
crosslinking, catalyzed with Pt-catalysts, of multiply
ethylenically unsaturated groups, preferably vinyl groups, of
substituted organopolysiloxanes with organopolysiloxanes multiply
substituted with Si--H groups in the presence of platinum
catalysts.
[0030] Preferably one of the components consists of
dialkylpolysiloxanes of the structure
R.sub.3SiO[--SiR.sub.2O].sub.n--SiR.sub.3 with n.gtoreq.0, wherein
the R residues have the meaning given above. Generally R is an
alkyl residue with 1 to 4 carbon atoms, wherein the alkyl residues
can be replaced completely or partially with aryl residues such as
the phenyl residue, and is replaced at one or both ends of one of
the terminal R residues with a polymerizable group such as the
vinyl group. R residues in the siloxane chain, also in combination
with the R residues of the end groups, can also partially be
replaced with polymerizable groups. Vinyl end-blocked
polydimethylsiloxanes of the structure
(CH.sub.2.dbd.CH.sub.2)R.sub.2SiO[--SiR.sub.2O].sub.n--SiR.sub.-
2(CH.sub.2.dbd.CH.sub.2) are preferably used.
[0031] The second component contains an Si--H-functional
crosslinking agent. The polyalkylhydrogensiloxanes usually employed
are copolymers of dialkylpolysiloxanes and
polyalkylhydrogensiloxanes with the general formula
R''.sub.3SiO[--SiR.sub.2O].sub.n--[SiHRO].sub.m--SiR''.sub.3 with
m.gtoreq.0, n.gtoreq.0 and with the proviso that at least two SiH
groups must be present, wherein R'' can have the meaning of H or R.
There are accordingly crosslinking agents with side and terminal
SiH groups, whereas siloxanes with R''.dbd.H, which only possess
terminal SiH groups, can also still be used for chain extension.
Small amounts of an organoplatinum compound are contained as
crosslinking catalyst.
[0032] Moreover, special silicone rubbers have also recently become
available commercially, which are crosslinked by means of the
addition reaction described, wherein special platinum complexes or
platinum/inhibitor systems are activated thermally and/or
photochemically and thus catalyze the crosslinking reaction.
[0033] Suitable materials also include silicone hybrid polymers.
Silicone hybrid polymers are copolymers or graft-copolymers of
organopolymer blocks, for example polyurethane, polyurea or
polyvinyl esters, and silicone blocks, generally based on
polydialkylsiloxanes of the aforementioned specification. For
example, thermoplastic silicone hybrid polymers are described in EP
1412416 B1 and EP 1489129 B1, the relevant disclosure of which is
also to be the subject matter of this application. Silicone hybrid
polymers of this kind are designated as thermoplastic silicone
elastomers (TPSE) and are available commercially. Other suitable
materials are (condensation or radiation) crosslinkable silicone
hybrid materials, as described in WO 2006/058656, the relevant
information on which is incorporated by reference in this
application.
[0034] Silicone resins are also suitable materials for the
production of the transparent or translucent coating. Generally the
silicone resins contain units with the general formula
R.sub.b(RO).sub.cSiO(.sub.4-b-c)/2, in which b is equal to 0, 1, 2
or 3, c is 0, 1, 2 or 3, with the proviso that b+c.ltoreq.3, and R
with the meaning given above, which form a highly crosslinked
organosilicone network structure. The silicone resins used can be
solvent-free, solvent-containing or can be used as aqueous systems.
Furthermore, it is also possible to use functionalized silicone
resins, e.g. those functionalized with epoxy or amine groups.
[0035] Silicone gels are also suitable materials for the production
of the transparent or translucent coating. Silicone gels are
prepared from two castable components, which crosslink at room
temperature in the presence of a catalyst. One of the components
generally consists of dialkylpolysiloxanes with the structure
R.sub.3SiO[--SiR.sub.2O].sub.n--SiR.sub.3 with n.gtoreq.0 and R
with the meaning given above, generally with 1 to 4 carbon atoms in
the alkyl residue, wherein the alkyl residues can be replaced
completely or partially with aryl residues such as the phenyl
residue, and is replaced with a polymerizable group such as the
vinyl group at one or at both ends of one of the terminal R
residues. Moreover, R residues in the siloxane chain, also in
combination with the R residues of the end groups, can be replaced
partially with polymerizable groups. Vinyl end-blocked
polydimethylsiloxanes of the structure
(CH.sub.2.dbd.CH.sub.2)R.sub.2SiO[--SiR.sub.2O].sub.n--SiR.sub.2(CH.sub.2-
.dbd.CH.sub.2) are preferably used.
[0036] The second component contains an Si--H-functional
crosslinking agent. The polyalkylhydrogensiloxanes usually employed
are copolymers of dialkylpolysiloxanes and
polyalkylhydrogensiloxanes with the general formula
R''.sub.3SiO[--SiR.sub.2O].sub.n--[SiHRO].sub.m--SiR''.sub.3 with
m.gtoreq.0, n.gtoreq.0 and with the proviso that at least two SiH
groups must be present, wherein R'' can have the meaning of H or R.
Accordingly there are crosslinking agents with side and terminal
SiH groups, whereas siloxanes with R''.dbd.=H, which only possess
terminal SiH groups, can also still be used for chain extension.
Small amounts of an organoplatinum compound are contained as
crosslinking catalyst. The crosslinking reaction is initiated by
mixing the components, and the gel is formed. This crosslinking
reaction can be accelerated by the action of heat and/or by
electromagnetic radiation, preferably UV radiation.
[0037] A detailed review of silicones, their chemistry, formulation
and application properties is given for example in
Winnacker/Kuchler, "Chemische Technik: Prozesse and Produkte, Vol.
5: Organische Zwischenverbindungen, Polymere", p. 1095-1213,
Wiley-VCH Weinheim (2005).
[0038] The morphology of the surface of the silicone coating is
important for the inhibition or prevention of fouling with
microorganisms. The surface morphology is determined from the
contact angle of said surface with water. The contact angle
according to the invention is adjusted by selection of the silicone
materials according to the invention. Further measures for
increasing the contact angle, for example roughening of the surface
(e.g. to simulate the so-called lotus effect), are preferably
ignored. In fact such roughening can disturb the cultivation of
phototrophic microorganisms. Surfaces with contact angles between
100.degree. and 120.degree. are preferred, surfaces with contact
angles between 100.degree. and 115.degree. are especially
preferred, and surfaces with contact angles between 100.degree. and
113.degree. are quite especially preferred. The contact angle of
the surface of the silicone coating with water can be determined by
methods known by a person skilled in the art, for example according
to DIN 55660-2, using commercially available measuring instruments
for determination of the contact angle, for example the contact
angle measuring systems obtainable from the company Kruss.
[0039] The reactor parts that come into contact with the culture
medium, in particular the inside surfaces of the reactor walls, are
coated completely or partially, preferably completely, with the
aforementioned silicones. In a preferred embodiment, the reactor
fittings are also coated completely or partially with silicone. The
silicones are applied in liquid form, either as pure substance, as
solution or in aqueous emulsion. The viscosity of the liquid to be
applied for coating is preferably from 10 mPas to 300 000 mPas.
[0040] No additives that can be released from the coating, as is
usual in marine antifouling systems, are added to the silicones.
Application can be by the usual techniques, preferably brushing,
spraying, dipping, knife-coating, casting. Dipping and spraying are
especially preferred. However, for coating tubes, other methods can
also be used, e.g. sponge application, spinning, extrusion or
crosshead extrusion, and for level surfaces additionally
application by means of roll coating, roller coating or by the
lick-roll process.
[0041] Application preferably takes place directly on the reactor
parts or reactor fittings, without application of a primer coat.
Generally the thickness of the coating is 10 nm to 1000 .mu.m,
preferably 1 .mu.m to 100 .mu.m. Optionally, to improve adhesion of
the silicones, the reactor parts to be coated can be pretreated,
for example by corona treatment. Optionally the silicones can
contain usual additives for promoting adhesion or usual fillers for
improving the mechanical properties. These additives are preferably
used in maximum amounts such that the silicone coating remains
transparent or translucent.
[0042] Any organisms adhering to the coated surfaces can be removed
between the cultivation cycles by spraying for example with water,
ethanol or H.sub.2O.sub.2 without further mechanical treatment.
[0043] The photobioreactors coated with silicone according to the
invention minimize the deposition of the phototrophic organisms
that form, so that the flow conditions of the culture medium remain
constant, and the ideal light input for growth remains set to
maximum growth of the organisms to be cultivated. Moreover,
expenditure on cleaning between individual cultivation cycles and
on changing the phototrophic organisms to be cultivated is
minimized. This leads to substantial economic advantages on account
of shorter downtimes and lower cleaning costs.
[0044] Compared with conventional silicone-containing foul-release
coatings, as used for example for coating ships' hulls, the
silicones used according to the invention are characterized in that
there is no need for release substances, which are released from
the coating (e.g. silicone oil). Furthermore, there is no need to
apply intermediate layers (primer) for better adhesion and
mechanical properties of the recipes used in foul-release coatings.
Achievement of contact angles with water with values of at least
100.degree., by using appropriate silicone materials, on the one
hand reduces the accumulation of water on the silicone surface, and
on the other hand substances dissolved in water, which are formed
for example by stress situations during cultivation of algae, are
also kept away from the surface.
* * * * *